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Effect of Side Groove Geometry on Crack Propagation Behavior and K1SSC in DCB Test

Product Number: 51321-16341-SG
Author: Yuji Arai/Jun Nakamura/Hiroki Kamitani/Keiichi Kondo/Hisashi Amaya/Taishi Fujishiro
Publication Date: 2021
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The double-cantilever beam (DCB) test method standardized in NACE TM0177-2016 is being increasingly applied as a quality assurance test to specify the performance of carbon and low-alloy steels for the sour service. The DCB test can contribute to the quantitative evaluation of the fracture toughness in a specific environment by assessing the crack arrest of a pre-cracked specimen. The test method has been discussed from the viewpoint of specimen geometries, such as side-groove root configurations, which are considered to change the stress concentration and thereby prevent the edge crack occurrence. In this paper, the DCB test was conducted with the current standard V-type and a proposed U-type side-groove configuration in order to compare crack propagation behaviors, by using in-situ ultrasonic observations and K1SSC values with 110 ksi sour grade material in a simulated sour environment. Crack propagation began a few hours after initiation of the test in NACE Solution A saturated with 1 bar H2S gas. The crack propagation rate and the final crack length were similar between the DCB specimens with the V-type and U-type side grooves. The obtained K1SSC values were almost the same, regardless of the side-groove configuration. In addition, the frequency of edge cracks for DCB specimens with theU-type side groove was lower than that of those with the V-type side groove. Therefore, it is appropriate to use the proposed U-type side-groove configuration for the DCB test.

Key words: Double Cantilever Beam, Sulfide stress cracking, FEA, K1SSC, NACE TM0177-2016 Method D, Compliance, Crack start position. 

The double-cantilever beam (DCB) test method standardized in NACE TM0177-2016 is being increasingly applied as a quality assurance test to specify the performance of carbon and low-alloy steels for the sour service. The DCB test can contribute to the quantitative evaluation of the fracture toughness in a specific environment by assessing the crack arrest of a pre-cracked specimen. The test method has been discussed from the viewpoint of specimen geometries, such as side-groove root configurations, which are considered to change the stress concentration and thereby prevent the edge crack occurrence. In this paper, the DCB test was conducted with the current standard V-type and a proposed U-type side-groove configuration in order to compare crack propagation behaviors, by using in-situ ultrasonic observations and K1SSC values with 110 ksi sour grade material in a simulated sour environment. Crack propagation began a few hours after initiation of the test in NACE Solution A saturated with 1 bar H2S gas. The crack propagation rate and the final crack length were similar between the DCB specimens with the V-type and U-type side grooves. The obtained K1SSC values were almost the same, regardless of the side-groove configuration. In addition, the frequency of edge cracks for DCB specimens with theU-type side groove was lower than that of those with the V-type side groove. Therefore, it is appropriate to use the proposed U-type side-groove configuration for the DCB test.

Key words: Double Cantilever Beam, Sulfide stress cracking, FEA, K1SSC, NACE TM0177-2016 Method D, Compliance, Crack start position. 

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Product Number: 51321-16407-SG
Author: Shiladitya Paul
Publication Date: 2021
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